I am going to paint (white/semi gloss) the interior of my Andersen picture window. Presently it is stained oak color & polyurethaned (sic) and furniture polish applied routinely for the past 25 years. How should I prepare the surface prior to painting?
Before beginning any prep protect the glass with safe release painters masking tape.
First thing to do is clean off the wax from all of the polishing. This will take a solvent to get a clean surface. A liquid sander like Paso will do this or use mineral spirits.
Next, sand all of the wood surfaces. Using a medium/fine sanding sponge rough up all areas needing paint. Wipe off the dust with a clean rag.
Now you can prime the window with an oil base wood primer.
That's it. The key is getting all of the wax off from the polish and sanding.